Advancements in the fields of radiation therapy and radiation protection are hindered by our lack of a thorough understanding of molecular events that underlie the radiation response of cells. One reason is the shortage of specialized instrumentation required by such studies on very small time and spatial scales. The inability to deliver radiation on microscopic scale can be especially detrimental when the radiation response of one or a few cells needs to be distinguished from that of an entire cell population. Many believe that long term radiation sequelae-that may not manifest themselves for decades-are regulated by events in signaling pathways, DNA damage assessment and repair, all occurring within the first few minutes following irradiation. To provide the much needed new cellular irradiation technology we propose to develop nanotechnology based microbeam array devices that can deliver low LET electron irradiation to individual cells in vitro simultaneous with real-time microscopic observation. Based on the unique field emission property of carbon nanotube the device delivers radiation from its 10,000 individually controlled microbeam-producing pixels. Radiation delivery can be spatially discreet or uniform, continuous or pulsed at a less than microsecond time scale. Most important from a radiation safety standpoint, the microbeams cause negligible radiation exposure to the operator, thus the devices do not require special shielding. Once developed, the Petri-dish- sized microbeam devices can become available to many laboratories to study molecular targets for the development of new radiosensitizers and radioprotectors. Specifically, in this proposal we propose to 1) determine specifications for the microbeam devices for cellular research; 2) perform fabrication and commissioning of a prototype single pixel microbeam device; 3) demonstrate the feasibility of the microbeam device in specific in vitro experiments including analyzing spatio-temporal regulation of EGFR, Ras, and MEKK pathways; and 4) develop and fabricate a multi-pixel microbeam array device. Together with the use of new biomarkers and cellular imaging techniques, the proposed device promises to open up new research capabilities for the identification and manipulation of radiation responses - an understanding vital to improvements in cancer therapy, the protection of astronauts on deep-space missions, and the protection of emergency-responders and the public against radiological terrorism. [unreadable] [unreadable]